A standard carburetor needle has five adjustable e-clip positions that move in increments of .040" ( forty thousandths of an inch ) at a time. This large adjustment can take you from too rich to too lean ( or visa versa ). The 5/20 Shim Kit allows you to adjust your needle .010" ( ten thousandths ) at a time giving you a total of 20 adjustments instead of just five. The 5/20 Shim Kit is easy to install and use.